A Correction Ratio Approach to Fission Matrix Interpolation in Systems with Large Temperature Differences

In this work, the Fission Matrix (FM) method is applied to Heat-Pipe Micro-Reactors (HPMRs). A set of FMs is generated through core simulations performed with the Serpent code, producing a database of ma trices corresponding to different uniform temperature conditions. This database enables the construction of interpolated FMs for arbitrary temperature distributions within the reactor core. To address the limitation of local temperature dependence, where interpolation considers only the temperature of the cell in which the fission event occurs, neglecting the influence of surrounding assemblies, a correction approach is intro duced: a correction ratio is defined to mitigate this assumption and improve interpolation accuracy. Several Test cases demonstrate the systematic improvement achieved in estimating the effective multiplication fac tor (keff) and the fission source distribution (F) when applying the proposed method. The results outcome of this work extends the applicability of the FM method for reactor, like HPMRs, being under variying thermal conditions, even off-design conditions, supporting more reliable reactor design and safety analysis.